Lake Tahoe Moving Beyond the Conflict:


	Water Quality Scientists at the University of California, Davis Conduct Research on the Source, Fate and Transport of the Controversial Gasoline Additive MTBE in a High Mountain, Recreational Lake Discovery of the gasoline additive methyl tert-butyl ether (MTBE) in groundwater, and lakes and reservoirs used for drinking water has raised considerable concern among public health officials and water suppliers in California. MTBE is a fuel oxygenate which enhances the octane in gasoline and decreases carbon monoxide emission by increasing burning efficiencies. The U. S. Environmental Protection Agency has classified MTBE as a possible human carcinogen and has a draft health advisory for drinking water of 20 to 200 痢/l or parts per billion (ppb). California state action levels have been established at 35 ppb. Recent, nation-wide sampling programs conducted by the U.S. Geological Survey have detected MTBE in both groundwater and stormwater. Possible sources of MTBE in shallow groundwater include direct contamination from leaking storage tanks and indirect contamination from stormwater flow and precipitation which washes through the urban atmosphere. Because of MTBE's possible health affects and the fact that it is highly soluble in water and difficult to biodegrade, its potential persistence in surface water supplies has recently raised public and legislative concern as well as numerous questions requiring additional research. As part of California's response to this issue, the Legislature recently passed SB 521 introduced by Sen. Richard Mountjoy (R-San Gabriel). This bill appropriates $500,000 to the University of California to assess the risks and benefits to human health and the environment of MTBE and its combustion byproducts found in air, water and soil. Among the numerous items contained in this bill is the requirement for an analysis of current levels of MTBE in the state's drinking water, reservoir, lakes and streams, and particularly in Lake Tahoe. Since March 26, 1997 lake water quality scientists from the Tahoe Research Group (TRG) at the University of California, Davis have been studying sources, transport and fate of MTBE in Donner Lake. Donner Lake is located at the summit of Interstate 80 as it passes through the Sierra Nevada in California and is 12 miles northwest of the renown Lake Tahoe. Donner Lake lies at an elevation of 5,936 feet above sea level with a surface area of 1.5 square miles. It's volume is approximately 102,000 acre-feet with a maximum depth of 230 feet and an average depth of 109 feet. Among its designated beneficial uses Donner Lake is a source of drinking water, contact and non-contact water recreation, sportfishing, freshwater and spawning habitat for coldwater fish, and downstream its water support habitat necessary for the survival and maintenance of fish species listed under law as threatened and/or endangered. The UC Davis-TRG project began at the request of the California Fish & Game Department to evaluate lake response to a leak in a major fuel pipeline. On March 1st fuel containing MTBE was discovered draining into Summit Creek, the main stream feeding into Donner Lake. The UCD-TRG scientific team headed by Dr. John E. Reuter, Dr. Charles R. Goldman, Brant C. Allen and Bob Richards, and Scott Seyfried a senior scientist with the firm of Levine-Fricke-Recon (Roseville, CA), have sampled the lake on 12 occasions since late-March. In total, nearly 500 individual lake water samples have been analyzed for MTBE. In cooperation with Dr. Roger Scholl, Laboratory Director for Alpha Analytical, Inc. a commercial water quality laboratory in Sparks, NV, high sensitivity detection limits of 0.1 ppb were achieved specifically for this research effort. According to Dr. Reuter, a member of the research faculty at UC Davis and Director of the Lake Tahoe Interagency Monitoring Program, "our effort to date at Donner Lake represents one of the most extensive field studies of MTBE in lakes in the nation". The sampling effort was designed in a systematic manner in order to answer a number of important questions including: the contribution of the fuel spill on MTBE in Donner Lake; the relative contribution of recreational water craft (2-cycle engines) as a source of MTBE, the extent of MTBE transport from surface waters into deeper portions of the lake, the loss rate of MTBE from the water column, persistence of MTBE during the fall and winter, and influence of meteorological factors such as air and water temperature, wind velocity and atmospheric pressure on MTBE distribution. The UCD-TRG researchers and their collaborators are discussing the funding of this project with both state and federal water quality and water resources agencies. According to Dr. Reuter and UCD scientist Brant Allen, published reports by agency and research institutions have primarily focused on MTBE in groundwater and urban runoff. Numerous scientific papers are now published which estimate the residence time of MTBE in lakes and streams based on theoretical calculations. The UCD-TRG scientific team considers data sets such as theirs on Donner Lake to be critical to modeling efforts which attempt predict the fate and transport of MTBE in aquatic systems. They report that many of the characteristics that affect the distribution of MTBE in natural waters require comprehensive field studies which take whole-lake physical, chemical and biological processes into account. Both Dr. Reuter and Dr. Goldman stress that investigations designed simply to measure existing concentrations of MTBE in water bodies either from surface waters or at a limited number of depths, or from those areas likely to show higher MTBE concentrations (e.g. in the vicinity of marinas) tell us the worse case scenario only and shed little light on the persistence and dynamics of this compound. Highlights from the ongoing UCD-TRG research at Donner Lake have indicated the following: * Of the 470 samples analyzed to date MTBE concentrations have ranged from 0.09 to 12.1 ppb. * Concentrations of MTBE appear to be uniformly distributed throughout the entire surface area of the lake. * Residual concentrations carried over from 1996 to 1997 are in the range of 0.1-0.2 ppb. * Approximately 30 days after the Summit Creek fuel spill, MTBE in Donner Lake was only 0.3-0.4 ppb suggesting no significant impact. * Beginning in early May, and coincident with the onset of the summer boating season, MTBE concentrations in the surface waters increased from a low value of 0.1 ppb on April 24th to approximately 2 ppb just prior to the 4th of July weekend. * Sampling on July 7th showed a dramatic 6-fold increase of MTBE in surface water from 2 to 12 ppb. This increase is most likely the result of increased fuel exhaust into Donner Lake from 2-cycle engine watercraft since rainfall and urban runoff was negligible at this time, and since stream flow was nearing its seasonal minimum. * MTBE in the upper and warmer portion of the lake (0-35 feet deep) was uniformly high as the result of natural wind mixing of these waters. Below approximately 50 feet in the colder uncirculated waters MTBE was always less than 0.5 ppb. This distinct distribution results from the formation of a stable density boundary in the lake which prevents mixing between the surface and bottom waters. * During March and April, before boating activity increased on the lake, it was calculated that Donner Lake contained 45-65 pounds of MTBE. By July 1st this had increased to 250 pounds with a sharp increase to the maximum of 815 pounds shortly after the July 4th holiday. Over the September 1st Labor Day weekend MTBE also increased but much less dramatically (i.e. approximately a 100 pound increase). * Despite a number of increases and decreases during the summer, the whole lake content of MTBE is on a slow decline with a projected half-life on the order of 80-120 days. In a statement delivered to the Tahoe Regional Planning Agency earlier this year during controversial debates on the banning of personal watercraft and other 2-cycle engines from the waters of Lake Tahoe, Dr. Goldman and his colleagues briefed the Governing Board and stressed the importance of the following factors in assessing the impacts of MTBE on Lake Tahoe water quality: (1) determine extent of watercraft use, (2) measure magnitude of unburned engine emissions, (3) determine the amount of emissions that are solubilized in lake water, (4) understanding fate and transport of MTBE in lakes and other water bodies, and (5) determining risk to human health and aquatic life. The UCD scientists emphasize the importance of the type of research being done at Donner Lake to policy decisions on lakes throughout California and elsewhere oxygenated fuels containing MTBE are being used. Despite current funding difficulties the UCD-TRG team and their collaborators will continue their research at Donner Lake until the spring in order to cover a complete annual cycle. According to Dr. Reuter, "our research at Donner Lake has broad applicability and transferability to other lakes both within California and nationally. We hope to be able to combine our field research with our ongoing modeling efforts to more fully understand the impact of MTBE in freshwaters". For more information contact: Dr. John E. Reuter Tahoe Research Group University of California, Davis One Shields Avenue Davis, CA 95616 e-mail: jereuter@ucdavis.edu phone: (916) 758-3327 Voice mail: (916) 759-1322 Fax (916) 753-8407